System and method for heating and cooling

ABSTRACT

An HVAC system is provided. Embodiments of the present disclosure generally relate to an HVAC system in which multiple indoor units are coupled to central outdoor unit, where at least one of the indoor units is configured to provide conditioned air through ductwork and at least one indoor unit is configured to provide conditioned air without ductwork. Moreover, a gas furnace can be provided in the system, for harsher environments that benefit from more robust heating. Additional systems, devices, and methods are also disclosed.

BACKGROUND

This section is intended to introduce the reader to various aspects ofthe art that may be related to various aspects of the presentlydescribed embodiments—to help facilitate a better understanding ofvarious aspects of the present embodiments. Accordingly, it should beunderstood that these statements are to be read in this light, and notas admissions of prior art.

Modern residential and industrial customers expect indoor spaces to beclimate controlled. In general, heating, ventilation, andair-conditioning (“HVAC”) systems circulate an indoor space's air overlow-temperature (for cooling) or high-temperature (for heating) sources,thereby adjusting the indoor space's ambient air temperature. HVACsystems generate these low- and high-temperature sources by, among othertechniques, taking advantage of a well-known physical principle: a fluidtransitioning from gas to liquid releases heat, while a fluidtransitioning from liquid to gas absorbs heat.

Within a typical HVAC system, a fluid refrigerant circulates through aclosed loop of tubing that uses compressors and other flow-controldevices to manipulate the refrigerant's flow and pressure, causing therefrigerant to cycle between the liquid and gas phases. Generally, thesephase transitions occur within the HVAC's heat exchangers, which arepart of the closed loop and designed to transfer heat between thecirculating refrigerant and flowing ambient air. As would be expected,the heat exchanger providing heating or cooling to theclimate-controlled space or structure is described adjectivally as being“indoors,” and the heat exchanger transferring heat with the surroundingoutdoor environment is described as being “outdoors.”

The refrigerant circulating between the indoor and outdoor heatexchangers—transitioning between phases along the way—absorbs heat fromone location and releases it to the other. Those in the HVAC industrydescribe this cycle of absorbing and releasing heat as “pumping.” Tocool the climate-controlled indoor space, heat is “pumped” from theindoor side to the outdoor side. And the indoor space is heated by doingthe opposite, pumping heat from the outdoors to the indoors.

Many North American residences employ “ducted” systems, in which astructure's ambient air is circulated over a central indoor heatexchanger and then routed back through relatively large ducts (orductwork) to multiple climate-controlled indoor spaces. However, the useof a central heat exchanger can limit the ducted system's ability tovary the temperature of the multiple indoor spaces to meet differentoccupants' needs. This is often resolved by increasing the number ofseparate systems within the structure—with each system having its ownoutdoor unit that takes up space on the structure's property, which maynot be available or at a premium.

Residences outside of North America often employ “ductless” systems, inwhich refrigerant is circulated between an outdoor unit and one or moreindoor units to heat and cool specific indoor spaces. Unlike ductedsystems, ductless systems route conditioned air to the indoor spacedirectly from the indoor unit—without ductwork. Typically, ductlesssystems are suited for moderate climates, and are not optimal forclimates where robust heating of the indoor space may be desired.

SUMMARY

Certain aspects of some embodiments disclosed herein are set forthbelow. It should be understood that these aspects are presented merelyto provide the reader with a brief summary of certain forms theinvention might take and that these aspects are not intended to limitthe scope of the invention. Indeed, the invention may encompass avariety of aspects that may not be set forth below.

Embodiments of the present disclosure generally relate to an HVAC systemin which multiple indoor units are coupled to central outdoor unit,where at least one of the indoor units is configured to provideconditioned air through ductwork and at least one indoor unit isconfigured to provide conditioned air without ductwork. Advantageously,using a central outdoor unit for both the ducted and ductless indoorunits reduces the total amount of the structure's property used by theHVAC system, for example. Moreover, a gas furnace can be provided in thesystem, for harsher environments that benefit from more robust heating.

Various refinements of the features noted above may exist in relation tovarious aspects of the present embodiments. Further features may also beincorporated in these various aspects as well. These refinements andadditional features may exist individually or in any combination. Forinstance, various features discussed below in relation to one or more ofthe illustrated embodiments may be incorporated into any of theabove-described aspects of the present disclosure alone or in anycombination. Again, the brief summary presented above is intended onlyto familiarize the reader with certain aspects and contexts of someembodiments without limitation to the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of certain embodimentswill become better understood when the following detailed description isread with reference to the accompanying drawings in which likecharacters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates schematically an HVAC system for heating and coolingindoor spaces within a structure, in accordance with an embodiment ofthe present disclosure;

FIG. 2 is a schematic process-and-instrumentation drawing of an HVACsystem for heating and cooling indoor spaces within a structure, inaccordance with an embodiment of the present disclosure; and

FIG. 3 is a schematic electrical diagram illustrating a command andcontrol communication network for an HVAC system, in accordance with anembodiment of the present disclosure.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present disclosure will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed. It should be appreciated that in the development of any suchactual implementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments, the articles “a,”“an,” “the,” and “said” are intended to mean that there are one or moreof the elements. The terms “comprising,” “including,” and “having” areintended to be inclusive and mean that there may be additional elementsother than the listed elements.

Turning now the figures, FIG. 1 illustrates an HVAC system 10 inaccordance with one embodiment. As depicted, the system 10 providesheating and cooling for a residential structure 12. But the conceptsdisclosed herein are applicable to a myriad of heating and coolingsituations, including industrial and commercial settings.

The described HVAC system 10 divides into two primary portions: Theoutdoor unit 14, which mainly comprises components for transferring heatwith the environment outside the structure 12; and the indoor units 16 &17, which mainly comprise components for transferring heat with the airinside the structure 12. In the illustrated structure, a ducted indoorunit 16 and ductless indoor units 17 provide heating and cooling tovarious indoor spaces 28.

Focusing on the ducted indoor unit 16, it has an air-handler unit (orAHU) 24 that provides airflow circulation, which in the illustratedembodiment draws ambient indoor air via returns 26, passes that air overone or more heating/cooling elements (i.e., sources of heating orcooling), and then routes that conditioned air, whether heated orcooled, back to the various climate-controlled spaces 28 through ductsor ductworks 30—which are relatively large pipes that may be rigid orflexible. A blower 32 provides the motivational force to circulate theambient air through the returns 26, AHU, and ducts 30.

As shown, the ducted indoor unit 16 is a “dual-fuel” system that hasmultiple heating elements. A gas furnace 34, which may be locateddownstream (in terms of airflow) of the blower 32, combusts natural gasto produce heat in furnace tubes (not shown) that coil through thefurnace. These furnace tubes act as a heating element for the ambientindoor air being pushed out of the blower 32, over the furnace tubes,and into the ducts 30. However, the furnace is generally operated whenrobust heating is desired. During conventional heating and coolingoperations, air from the blower 32 is routed over an indoor heatexchanger 20 and into the ductwork 30. The blower, gas furnace, andindoor heat exchanger may be packaged as an integrated AHU, or thosecomponents may be modular. Moreover, it is envisaged that the positionsof the gas furnace and indoor heat exchangers or blower can be reversedor rearranged.

The indoor heat exchanger 20—which in this embodiment for the ductedindoor unit 16 is an A-coil 19, as it known in the industry—can act as aheating or cooling element that add or removes heat from the structureby manipulating the pressure and flow of refrigerant circulating withinand between the A-coil 19 and the outdoor unit 14 via refrigerant lines18.

In the illustrated embodiment of FIG. 1 , the state of the A-coil 19(i.e., absorbing or releasing heat) is the opposite of the outdoor heatexchanger 22. More specifically, if heating is desired, the illustratedindoor heat exchanger 20 acts as a condenser, aiding transition of therefrigerant from a high-pressure to gas to a high-pressure liquid andreleasing heat in the process. And the outdoor heat exchanger 22 acts asan evaporator, aiding transition of the refrigerant from a low-pressureliquid to a low-pressure gas, thereby absorbing heat from the outdoorenvironment. If cooling is desired, the outdoor unit 14 has flow-controldevices 38 that reverse the flow of the refrigerant—such that theoutdoor heat exchanger acts as a condenser and the indoor heat exchangeracts as an evaporator. The outdoor unit 22 also contains otherequipment—like a compressor 36, which provides the motivation forcirculating the refrigerant, and electrical control circuitry 64, whichprovides command and control signals to various components of the system10.

The outdoor unit 14 is a side-flow unit that houses, within a plastic ormetal casing or housing 48, the various components that manage therefrigerant's flow and pressure. This outdoor unit 14 is described as aside-flow unit because the airflow across the outdoor heat exchanger 22is motivated by a fan that rotates about an axis that isnon-perpendicular with respect to the ground. In contrast, “up-flow”devices generate airflow by rotating a fan about an axis generallyperpendicular to the ground. (As illustrated, the X-axis isperpendicular to the ground.) In one embodiment, the side-flow outdoorunit 14 may have a fan 50 that rotates about an axis that is generallyparallel to the ground. (As illustrated, the Y- and Z-axes are parallelto the ground.) It is envisaged the either up-flow or side-flow unitscould be employed. Advantageously, the side-flow outdoor unit 14provides a smaller footprint than traditional up-flow units, which aremore cubic in nature

In addition to the ducted indoor unit 16, the illustrated HVAC systemhas ductless indoor units 17 that also circulate refrigerant, via therefrigerant lines 18, between the outdoor heat exchanger 22 and theductless indoor unit's heat exchanger. The ductless indoor units 17 maywork in conjunction with or independent of the ducted indoor unit toheat or cool the given indoor space 28. That is, the given indoor space28 may be heated or cooled with the structure's air that has beenconditioned by the ductless indoor unit 17 and by the air routed throughthe ductwork 30 after being conditioned by the A-coil 19, or it may beentirely conditioned by the air coil or the ducted indoor unit workingindependent of one another. As another embodiment, the A-coilrefrigerant loop may be operated to provide cooling or heating only—andthe ductless indoor units may also be designed to provide cooling orheating only.

FIG. 2 provides further detail about the various components of an HVACsystem and their operation. The compressor 36 draws in gaseousrefrigerant and pressurizes it, sending it into the closed refrigerantloop 18 via compressor outlet 52. (A flow meter 53 may be used tomeasure the flow of refrigerant out of the compressor.) The outlet 52 isconnected to a reversing valve 54, which may be electronic, hydraulic orpneumatic and which controls the routing of the high-pressure gas to theindoor or outdoor heat exchangers. Moreover, the outlet 52 may becoupled to an oil separator 55 that isolates oil expelled by thecompressor and, via a return line 51, returns the separated oil to thecompressor inlet 62—to help prevent that expelled oil from reaching thedownstream components and helping ensure the compressor maintainssufficient lubrication for operation. The oil return line 51 may includea valve 57 that reduces the pressure of the oil returning to thecompressor 36.

To cool the structure, the high-pressure gas is routed to the outdoorheat exchangers 22, where airflow generated by the fans 50 aids thetransfer of heat from the refrigerant to the environment—causing therefrigerant to condense into a liquid that is at high-pressure. Asshown, the outdoor unit 14 has multiple heat exchangers 22 and fans 50connected in parallel, to aid the HVAC system's operation.

The refrigerant leaving the heat exchangers 22 is or is almost entirelyin the liquid state and flows through or bypasses a metering device 61.From there, the high-pressure liquid refrigerant flows into a series ofreceiver check valves 58 that manage the flow of refrigerant into thereceiver 42. The receiver 42 stores refrigerant for use by the systemand provides a location where residual high-pressure gaseous refrigerantcan transition into liquid form. And the receiver may be located withinthe casing 48 of the outdoor unit or may be external to the casing 48 ofthe outdoor unit. (Or the system may have no receiver at all.) From thereceiver 42, the high-pressure liquid refrigerant flows to the indoorunits 16, 17, specifically to metering devices 60 that restrict the flowof refrigerant into each heat exchanger 16, 17, to reduce therefrigerant's pressure. The refrigerant leaves the indoor meteringdevices 60 as a low-pressure liquid. In the described embodiment, themetering device 60 is an electronic expansion valve, but other types ofmetering devices—like capillaries, thermal expansion valves, reducedorifice tubing—are also envisaged. Electronic expansion valves provideprecise control of refrigerant flow into the heat exchangers of theindoor units, thus allowing the indoor units—in conjunction with thecompressor—to provide individualized cooling for the given indoor space28 the unit is assigned to.

Low-pressure liquid refrigerant is then routed to the indoor heatexchangers 20. As illustrated, the indoor heat exchanger 20 for theducted indoor unit 16 is an “A-coil” style heat exchanger 19. Airflowgenerated by the blower 32 aids in the absorption of heat from theflowing air by the refrigerant, causing the refrigerant to transitionfrom a low-pressure liquid to a low-pressure gas as it progressesthrough the indoor heat exchanger 20. And the airflow generated by theblower 32 drives the now cooled air into the ductwork 30, cooling theindoor spaces 28. In a similar fashion, the low-pressure liquidrefrigerant is routed to the indoor heat exchangers 20 of the ductlessindoor units 17, where it is evaporated, causing the refrigerant toabsorb heat from the environment. However, unlike the ducted indoorunit, the ductless indoor units circulate air without ductwork, using alocal fan 50, for example.

The refrigerant leaving the indoor heat exchangers 20, which is nowentirely or mostly a low-pressure gas, is routed to the reversing valve54 that directs refrigerant to the accumulator 46. Any remaining liquidin the refrigerant is separated in the accumulator, ensuring that therefrigerant reaching the compressor inlet 62 is almost entirely in agaseous state. The compressor 36 then repeats the cycle, by compressingthe refrigerant and expelling it as a high-pressure gas.

For heating the structure 12, the process is reversed. High-pressure gasis still expelled from the compressor outlet 52 and through the oilseparator 55 and flow meter 53. However, for heating, the reversingvalve 54 directs the high-pressure gas to the indoor heat exchangers 20.There, the refrigerant—aided by airflow from the blower 32 or the fans50—transitions from a high-pressure gas to a high-pressure liquid,expelling heat. And that heat is driven by the airflow from the blower32 into the ductwork 30 or by the fans 50 in the ductless indoor units17, heating the indoor spaces 28. If more robust heating is desired, thegas furnace 34 may be ignited, either supplementing or replacing theheat from the heat exchanger. That generated heat is driven into theindoor spaces by the airflow produced by the blower 32 or the fans 50.

The high-pressure liquid refrigerant leaving each indoor heat exchanger20 is routed through or past the given metering valve 60, which is, inthis embodiment, an electronic expansion valve. But for otherembodiments, the valve may be any other type of suitable expansionvalve, like a thermal expansion valve or capillary tubes, for example.Using the refrigerant lines 18, the high-pressure liquid refrigerant isrouted to the receiver check valves 58 and into the receiver 42. Asdescribed above, the receiver 42 stores liquid refrigerant and allowsany refrigerant that may remain in gaseous form to condense. From thereceiver, the high-pressure liquid refrigerant is routed to an outdoormetering device 61, which lowers the pressure of the liquid. Just likethe indoor metering device 60, the illustrated outdoor metering device61 is an electrical expansion valve. But it is envisaged that theoutdoor metering device could be any number of devices, includingcapillaries, thermal expansion valves, reduced orifice tubing, forexample.

The lower-pressure liquid refrigerant is then routed to the outdoor heatexchangers 22, which are acting as evaporators. That is, the airflowgenerated by the fans 50 aids the transition of low-pressure liquidrefrigerant to a low-pressure gaseous refrigerant, absorbing heat fromthe outdoor environment in the process. The low-pressure gaseousrefrigerant exits the outdoor heat exchanger 22 and is routed to thereversing valve, which directs the refrigerant to the accumulator. Thecompressor 36 then draws in gaseous refrigerant from accumulator,compresses it, and then expels it via the outlet 52 as high-pressuregas, for the cycle to be repeated.

As illustrated in FIG. 2 , the system is a “two-pipe” variablerefrigerant flow system, in which the HVAC system's refrigerant iscirculated between the outdoor 14 and indoor units via two refrigerantlines 18, one of which is a line that carries predominantly liquidrefrigerant (a liquid line 66) and one of which is a line that carriespredominately gas refrigerant (a gas line 68). However, it is alsoenvisaged that, in other embodiments, aspects described herein could beapplied to a three-pipe variable refrigerant flow system, in which inaddition to the gas and liquid lines a third discharge lines aids in thecirculation of refrigerant.

In many instances, the structure 12 may have had a previous HVAC systemwith pre-existing refrigerant piping at least partially built into thestructure's interior walls. For example, the pre-existing system may bea traditional HVAC unit that uses circulating refrigerant for coolingonly and a gas furnace for heating, with all of the conditioned airdelivered to the interior spaces via the ductwork. And the pre-existingrefrigerant lines—which are built into the walls of the structure—mayhave a gas line with a 6/8 inch, ⅞ inch, or 9/8 inch outer diameter gasline. However, in certain embodiments, the outdoor unit 14 may have moremodern refrigerant piping, which tends to be smaller in outer diameter.For example, the outdoor unit 14 may be 2, 3, or 4 Ton unit that has agas line diameter of ⅝ inch. It would be laborious and cost ineffectiveto replace the pre-existing gas line in the structure with ⅝ inchdiameter tubing. Accordingly, the illustrated HVAC system includes acoupler 70 that helps couple the varying diameter gas lines to oneanother. For example, the coupler 70 may facilitate coupling of theoutdoor unit's ⅝ inch diameter gas line to the structure's pre-existing6/8 inch, ⅞ inch, 9/8 inch diameter gas line. In another embodiment, theoutdoor unit 14 may be a 5 Ton unit with a gas line having a diameter of6/8 inch. The coupler could facilitate coupling of this outdoor unitwith a pre-existing gas line of ⅞ inch or 9/8 inch diameter.

FIG. 3 illustrates the HVAC system 10 of FIG. 2 , but provides furtherinformation about the HVAC system's control architecture. Asillustrated, the HVAC system 10 includes one or more controllers 64 thatmanage the operating of the HVAC's system's components. Specifically,the illustrated system includes a controller 64(a) for the outdoor unit14, a controller 64(b) for the indoor air coil 19, controller 64(c) forthe gas furnace 34 and controllers 64(d) for the ductless indoor units17.

These controllers send command and control signals to a myriad ofcomponents within each controller's device and to each other. Forexample, the outdoor unit's controller 64(a) may receive input data froma wide variety of temperature and/or pressure sensors 72 providinginformation about the condition of the refrigerant or the surroundingenvironment. Moreover, the controller may be in communication withvarious components of the system—for example, the fan 50, the compressor36, the receiver 42—that send operation data (e.g., motor speed, liquidlevel in the receiver) to the controller.

In response to that information, the controller may determine the bestoperating parameters for various components in the system and provideappropriate commands. For example, the controller may actuate themetering device 61 to control the device's open or closed status. Or thecontroller may vary the operating speed for the fans 50 or compressor36. Similarly, the controllers 64(b), 64(c), 64(d) of the indoor unitprovide like data collection and operational commands to the componentsof their respective units.

Additionally, the controllers 64(a)-64(d) may be in communication withone another. In one embodiment, the outdoor unit's controller 64(a) canbe in communication with A-coil controller 64(b) with the twocontrollers communicating via a common protocol, like ClimateTalk. Andthe A-coil controller 64(b) may be communicating with the gas furnacecontroller 64(c), again via ClimateTalk, as one example of a protocol.

However, as illustrated, the ductless indoor unit's controllers 64(d)may be receiving data and providing command and control signals via adifferent protocol, like the P1/P2 protocol used by Daikin Industries,Ltd. Because the two controllers—64(b) and 64(d)—operate off ofdifferent protocols, the HVAC system includes translationsfeatures—which might be provided as hardware or through software storedin memory on the controllers—that facilitate communications between thedifferent protocols and, thus, the different controllers. As a result,the entire HVAC system is able to provide data and communicate andreceive and send command instructions as a unit, even though the systemis operating off of two or more protocols. In fact, the use of thetranslation features allows for new equipment, like the ductless indoorunits 17, to be installed in a structure that was originally designedand has equipment for a ducted system. In the past, installing theductless indoor units meant adding an additional outdoor unit that isdesigned to communicate over a P1/P2 protocol, for example, because theinstalled ducted system was designed to communicate over a ClimateTalkprotocol. Moreover, these command and control communications may be overa wired bus or network, or may be communicated over a wireless network.

As an alternative embodiment, the outdoor unit's controller 64(a) maycommunicate first with the controllers 64(d) of the indoor units over aprotocol like P1/P2. Then, using translation features as describedabove, the controller 64(d) of the indoor unit may communicate with thecontroller 64(b) of the A-coil, which may be operating off of aClimateTalk protocol.

The illustrated controllers 64 may be a programmable logic circuit or aprocessor or integrated circuit with memory, for example. As oneparticular example, one or more of the disclosed controllers 64 includesinverter circuitry that conditions a received electrical signal to varythe speed of the compressor's motor, thereby regulating the amount ofrefrigerant the compressor pumps. Moreover, the inverter circuitry—whichchanges the frequency of the current motivating various electroniccomponents like motors—can be used to control the speed of othercomponents, like fans 50 or blowers 32. It is believed that the invertercircuity can improve the efficiency of the HVAC system in comparison totraditional system, which operate the compressor motor at a single speedand in a binary (on/off) manner.

However, it is also envisaged that the command of the controllers couldbe centralized into one controller located in either the indoor oroutdoor units, or it could be decentralized to multiple controllerslocated throughout the HVAC system, or those controllers may be locatedat a remote location accessible through a network or the Internet.

With reference to FIGS. 1-3 , the illustrated HVAC system 10 can beoperated in manners that are believed to be beneficial. For example, thesystem may include an oil-recovery operation that reduces the amount oflubricant—such as mineral oil—resident outside of the compressor.Circulating refrigerant includes a small amount of lubricant, tolubricate the moving parts of the compressor. But the lubricant provideslittle benefit to the other components of the HVAC system. In fact,stray lubricant expelled by the compressor and circulated with therefrigerant can negatively impact the system's overall performance andreduce the amount of lubricant available to the compressor. To mitigatestray lubricant, the HVAC system has an “oil-recovery” mode, where thesystem operates to increase the flow velocity of the refrigerant, byincreasing the rotational speed of the compressor, to help carry thestray refrigerant back to the compressor 36, where it is removed by theoil separator 55. But, in the oil-recovery mode, the system may notprovide the heating or cooling functions desired in the indoor spaces28. Thus, activation of the oil-recovery mode is reduced.

In traditional systems, activation of the oil recovery mode is based onthe number of rotations of the compressor. That is, traditional systemsestimate the amount of stray oil in the system based on the number ofrotations of the compressor. However, the inventors have found thatmeasuring the number of compressor rotations does not provide anaccurate estimate of stray oil—often overestimating the amount andcausing the system to operate in an oil-recovery mode more frequentlythan necessary.

In the illustrated system, the amount of stray oil is estimated on thecirculation amount or flow rate of the refrigerant. This can becalculated by the controllers 64 using the myriad of input data from thesensors described above, or can be measured directly using a flow meter53. It is believed that estimating stray oil based on the circulationamount is more accurate, allowing the system to spend more timeaddressing the called for heating and cooling needs rather thantransitioning to and focusing on an oil-recovery mode.

As another advantage, the illustrated system can provide heating evenwhen the system is in a defrost mode. When the refrigerant iscirculating to provide heating to the structure, the outdoor heatexchanger 22 absorbs heat from the surrounding environment. If theoutside ambient temperature is low, this could cause moisture in the airto freeze onto the outdoor heat exchanger. The outdoor heat exchanger 22is defrosted by switching the system into a cooling state, causing theoutdoor exchanger 22 to become the condenser, which expels heat andmelts the accumulating ice. In the present system, because heating canbe provided via a gas furnace as well as the circulating refrigerant,the indoor space 28 may remain at the desired temperature, minimizingdiscomfort to the occupants.

In accordance with another embodiment, the system may include adew-prevention system that reduces the likelihood of condensationforming on the refrigerant lines, which can damage the structure. Forexample, the structure's previous HVAC system may have been used underdifferent operating conditions, conditions that did not necessitateinsulation of the pre-existing liquid line 66 to mitigate condensation(or dew) from forming on the line. And removing or replacing thepre-existing lines may not be economic or feasible.

The described HVAC system includes a methodology that uses data from thesystem's various sensors and controllers to prevent the formation ofdew. As the refrigerant travels through the uninsulated piping to heatthe structure, it cools, and may cool to the point that the nowcondensed liquid refrigerant's temperature is lower than the temperatureat which moisture in the surrounding air condenses on the piping,causing dew. In general, the risk for dew formation can be rudimentarilyquantified using the following formula:

((“Determined Dew Point Temperature [DDPT)−(RefrigerantTemperature[RT]))*(Length of Time RT<DDPT):

where DDTP is the calculated dew point, which may be based ontemperature and humidity sensors in the system measuring the surroundingenvironment, or may be provided by an external source in communicationwith the system; where RT is the measured temperature of the refrigerantat a downstream point in the line; and where Length of Time RT<DDPT isthe length of time the refrigerant temperature has been less than thedetermined dew point temperature.

Increasing the temperature of the refrigerant in the liquid line helpsto preclude dew formation. This is effected, in the heating mode, byactuating the outdoor unit's 14 electronic expansion valve 61, reducingits orifice size and restricting the flow of the liquid refrigerant intothe heat exchangers 22 that are acting as evaporators. Less refrigerantflow into the evaporators 22 “starves” them, causing the refrigerant totransition entirely to the gaseous stage at an earlier point in theevaporators. As a result, the refrigerant can continue to absorb heat asit flows through the evaporators and becomes more “superheated.” Andreturning gas refrigerant at a higher temperature to the accumulator 46causes the residual liquid in it to turn to gas, driving more of therefrigerant into circulation. Moreover, the controllers in the systemcan raise the expected superheat temperature of the refrigerant leavingthe evaporators, with the controller actuating the expansion valve 61 toreach the desired superheat temperature.

The combination of increased refrigerant circulation with restrictedflow of refrigerant into the evaporator causes an increase in the amountof liquid refrigerant in the liquid line. And, since that liquid cannotbe compressed, the overall temperature in the liquid line remains at ahigher temperature than if that valve 61 were less restricted.

As an additional measure, the controller may change the targettemperature for the refrigerant egressing the indoor units 20, which areacting as condensers, to reduce the amount of sub-cooling. Specifically,the controller 64 can effect operation of the expansion valves 60, 61and/or the compressor 36 to increase the temperature of the refrigerantleaving the condensers 20.

If one or more of the indoor units 16, 17 is not being asked to heat itsgiven indoor space 28, the expansion valve 60 of that unit can be openedfurther, to allow for the circulation of the refrigerant that may havebeen previously restricted. Concurrently, if the fans 50 in those unitsare operating to circulate air, the speed of those fans can be reduced,causing the temperature of the refrigerant in those units to increase.

As another measure, if the gas furnace 34 is active, the expansion valve60 of the ducted unit 16 can be opened to allow more refrigerant fromthe A-coil 19 to flow into the liquid line.

If the above-described actions are not having the desired effect, andthe RT remains close to the DDPT, the controller can send a signal tothe operating indoor unit 17, for example, to reduce the amount ofheating provided by the unit to the given indoor space 28. Moreover, thefan speed of that indoor unit can be reduced as well. This reduces theamount of heat that is transferred to the indoor space 28, heat thatremains in the circulating refrigerant.

Lastly, if all of the above-described mitigation techniques do notproduce the desired outcome, the controller 64 may be programmed todeactivate the system entirely, electing to cease heating operationsrather than potentially damaging the structure through dew formation.

Along the same lines, the system can be operated with dew-controlmethodology when in the cooling mode. For example, if the pressure ofthe refrigerant is less than the vapor pressure for the refrigerant atthe measured environmental temperature, that increases the change fordew formation. To mitigate this, the system can be programmed todecrease the fan speed of the operating outdoor unit, to increase thetemperature of the refrigerant in the liquid line.

It is envisaged that the foregoing described steps could be performedsequentially, or certain subsets of methods may be selected in varioussequences to effect the desired result.

There are number of refrigerants that can be used by the HVAC system.For example, the system 10 may circulate a single refrigerant, such asR32. Or the system may employ a composite of multiple refrigerants. Forexample, the system may employ refrigerants with the followingcomposition (by weight):

Composite R32 R125 R1234yf Refrigerant (%) weight) (%) weight) (%)weight) DR-55 67.0 7.0 26.0 R410 50.0 50.0 0.0 DR-5 72.5 0.0 27.5

As a another potential embodiment, the HVAC system may employ ahydrofluoro-olefin (HFO) refrigerant. The employed HFO refrigerant mayby of a single type or a composite. For example, the system may employHFO refrigerants with the following composition (by weight):

Composite HFO-1123 R32 Refrigerant (weight) (%) weight) HFO-Mix 1 45.055.0 HFO-Mix 2 40.0 60.0

While the aspects of the present disclosure may be susceptible tovarious modifications and alternative forms, specific embodiments havebeen shown by way of example in the drawings and have been described indetail herein. But it should be understood that the invention is notintended to be limited to the particular forms disclosed. Rather, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by thefollowing appended claims.

What is claimed is:
 1. A method for utilizing a dew-prevention system,the method comprising preventing or reducing dew condensation on aliquid line positioned between an indoor heat exchanger and an outdoorheat exchanger of a heating, ventilation, and air-conditioning (HVAC)system by: increasing a level of a liquid refrigerant in the liquidline; and increasing a temperature of the liquid refrigerant in theliquid line, wherein increasing the level and the temperature of theliquid refrigerant in the liquid line are achieved by decreasing a flowrate of the liquid refrigerant into the outdoor heat exchanger of theHVAC system operating as an evaporator in a heating mode.
 2. The methodof claim 1, wherein preventing or reducing dew condensation on theliquid line further comprises operating at least one controller tocontrol the temperature of the liquid refrigerant in the liquid linebased at least in part on data received from at least one sensor of theHVAC system.
 3. The method of claim 2, further comprising: determining arisk for dew condensation, wherein the risk is determined by theformula:Risk for dew condensation=((Determined Dew Point Temperature(“DDPT”))−(Refrigerant Temperature (“RT”)))*(Length of Time thatRT<DDPT),  wherein DDPT is a calculated dew point temperature based onat least one of the at least one sensor or an external source incommunication with the HVAC system,  wherein RT is a measuredtemperature of the liquid refrigerant in the liquid line, and  whereinLength of Time that RT<DDPT is a length of time that the measuredtemperature of the liquid refrigerant has been less than the calculateddew point temperature; and  controlling, via the at least onecontroller, the temperature of the liquid refrigerant in the liquid lineof the HVAC system based at least in part on the determined risk for dewcondensation.
 4. The method of claim 3, further comprising changing atarget temperature of the liquid refrigerant exiting the indoor heatexchanger by operating the controller to control at least one of a firstexpansion valve, a second expansion valve, or a compressor to reducesubcooling and to increase the temperature of the liquid refrigerant inthe liquid line following the indoor heat exchanger.
 5. The method ofclaim 3, wherein increasing the level and the temperature of the liquidrefrigerant in the liquid line further comprises the at least onecontroller controlling the indoor heat exchanger to reduce an amount ofheating provided to an indoor space than previously provided.
 6. Themethod of claim 3, further comprising operating the at least onecontroller to deactivate the HVAC system entirely to cease operationsdue to a formation of dew condensation on the liquid line.
 7. The methodof claim 1, wherein preventing or reducing dew condensation on a liquidline further comprises: opening an expansion valve when the indoor heatexchanger is not actively heating an indoor space to increasecirculation of a heat-absorbed refrigerant through the indoor heatexchanger; and concurrently reducing a speed of a fan blowing air overthe indoor heat exchanger such that an increased amount of heat remainsin the heat-absorbed refrigerant compared to not opening the expansionvalve and not reducing the speed of the fan.
 8. The method of claim 1,further comprising opening an expansion valve further to allow morerefrigerant to flow through the indoor heat exchanger when a gas furnaceis operating such that at least some heat from the gas furnace istransferred to the indoor heat exchanger and thus to the refrigerant inthe indoor heat exchanger, thus increasing the temperature of the liquidrefrigerant in the liquid line.
 9. A method of operating a heating,ventilation, and air-conditioning (HVAC) system comprising: operatingthe HVAC system in a heating mode whereby liquid refrigerant undergoesevaporation in an outdoor heat exchanger; and preventing or reducing dewcondensation, while in the heating mode, on a liquid line positionedbetween an indoor heat exchanger and the outdoor heat exchanger of theHVAC system by: restricting a flow of the liquid refrigerant into theoutdoor heat exchanger by reducing an orifice size of a first expansionvalve, thereby causing the liquid refrigerant to transition to a gaseousrefrigerant at an earlier point in the outdoor heat exchanger and becomesuperheated; and flowing the superheated gaseous refrigerant to anaccumulator, the superheat of which transitions residual liquidrefrigerant within the accumulator to a gaseous refrigerant, causingmore refrigerant to be in circulation than if the first expansion valvewere less restricted, wherein more refrigerant in circulation andrestricting the flow of the liquid refrigerant into the outdoor heatexchanger causes an increased level of the liquid refrigerant in theliquid line, and wherein the increased level of the liquid refrigerantin the liquid line and the inability of the increased level of theliquid refrigerant in the liquid line to be compressed causes anincreased temperature of the liquid refrigerant in the liquid line thanif the expansion valve were less restricted, thereby preventing orreducing dew condensation on the liquid line.
 10. The method of claim 9,wherein preventing dew condensation on the liquid line further comprisesoperating at least one controller to control the temperature of theliquid refrigerant in the liquid line based at least in part on datareceived from at least one sensor of the HVAC system.
 11. The method ofclaim 10, further comprising changing a target temperature of the liquidrefrigerant exiting the indoor heat exchanger by operating thecontroller to control at least one of a first expansion valve, a secondexpansion valve, or a compressor to reduce subcooling and to increasethe temperature of the liquid refrigerant in the liquid line followingthe indoor heat exchanger.
 12. The method of claim 10, whereinincreasing the level and the temperature of the liquid refrigerant inthe liquid line further comprises the at least one controllercontrolling the indoor heat exchanger to reduce an amount of heatingprovided to an indoor space than previously provided.
 13. The method ofclaim 10, further comprising operating the at least one controller todeactivate the HVAC system entirely to cease operations due to aformation of dew condensation on the liquid line.
 14. The method ofclaim 9, wherein preventing or reducing dew condensation on the liquidline further comprises: opening an expansion valve when the indoor heatexchanger is not actively heating an indoor space to increasecirculation of a heat-absorbed refrigerant through the indoor heatexchanger; and concurrently reducing a speed of a fan blowing air overthe indoor heat exchanger such that an increased amount of heat remainsin the heat-absorbed refrigerant compared to not opening the expansionvalve and not reducing the speed of the fan.
 15. The method of claim 9,further comprising opening an expansion valve further to allow morerefrigerant to flow through the indoor heat exchanger when a gas furnaceis operating such that at least some heat from the gas furnace istransferred to the indoor heat exchanger and thus to the refrigerant inthe indoor heat exchanger, thus increasing the temperature of the liquidrefrigerant in the liquid line.
 16. An HVAC system for providingconditioned air to a structure: an outdoor unit configured to operate acompressor at variable speeds; a plurality of indoor units configurableto provide conditioned air to the structure, wherein the plurality ofindoor units comprises: a ducted indoor unit comprising a firstexpansion valve for controlling refrigerant flow; and a ductless indoorunit comprising a second expansion valve for controlling refrigerantflow.
 17. The HVAC system of claim 16, wherein the outdoor unit isconfigured to couple to refrigerant piping that was previously coupledto a different outdoor unit.
 18. The HVAC system of claim 17, whereinthe outer diameter of the refrigerant piping in the structure thatconveys refrigerant in predominately in gas phase between the indoorunits and the outdoor unit is larger than the outer diameter of theoutdoor unit's corresponding piping for routing refrigerant inpredominately in gas phase.
 19. The HVAC system of claim 16, wherein therefrigerant comprises at least 50%, in terms of weight, R32 refrigerant.20. The HVAC system of claim 16, wherein the refrigerant at leastpartially comprises a hydrofluoro-olefin (HFO) refrigerant.
 21. The HVACsystem of claim 16, wherein the plurality of indoor units comprises aplurality of ductless indoor units.
 22. The HVAC system of claim 16,comprising an oil-recovery system configured to estimate an amount ofstray oil in the HVAC system based the flow rate of refrigerant in arefrigerant line coupling at least one of the indoor units to theoutdoor unit.